1. Field of the Invention
The presently disclosed subject matter relates to a system for measuring space width of joint, a method for measuring space width of joint and a recording medium, and particularly relates to the technique of aiding measurement in orthopedic surgery by detecting an anatomical feature point of a human body structure such as a center of a thigh femoral head, and measuring a space width of a joint of a hip joint and comparing images photographed at different times to make the images available for diagnosis of the temporal change of a disease in the hip joint and to perform quantification of evaluation of a space of the joint.
2. Description of the Related Art
Conventionally, diagnosis of a disease such as arthrosis deformans in a hip joint, a knee joint or the like has been performed mainly by X-ray images. In order to make the diagnosis or judgment by a doctor more accurate, it is necessary to provide objective diagnosis information of the position and the like of an anatomical feature point such as a center of a thigh femoral head (a thigh femoral head center), for example.
There is known the system which displays an image obtained by imaging a diagnosis object such as a pelvis, for example, on a display unit, receives information for drawing objects such as a reference line and a parallel line thereof for measuring bending of a body, for example, onto the image from an input unit, draws the objects on the image displayed on the display unit, calculates the value showing the geometric relationship between the drawn objects, and makes the value available for diagnosis of the doctor. The input information which is inputted from the input unit is a point on the image which is manually inputted by a user (doctor or the like), and the objects are drawn by directly using a positional information of the point which is inputted by the user (see, for example, Japanese Patent Application Laid-Open No. 2007-151742).
Further, in the diagnosis of a disease in a hip joint, comparison of a temporal changes of the minimum space width is very useful for diagnosis. There have been conventionally proposed various techniques of comparing images acquired over time, arranging a plurality of images, composing a plurality of images to form one image with high resolution, or displaying images by superimposing them on each other so that the shape of a subject is easily understood.
For example, there is known an image display device which obtains, from a distance calculated from a specific end point of at least any one of a diagnosis image and a reference image, a magnification (or reduction) ratio of the one image, and performs magnification or reduction processing of at least any one of the images so that the diagnosis image and the reference image have substantially the same size based on the ratio to reproduce and display both the images side by side at the same time (see, for example, Japanese Patent Application Laid-Open No. 9-56706).
Further, there is known an image composite method (see, for example, Japanese Patent Application Laid-Open No. 9-18685) in which distortion of each of images sequentially inputted is corrected, a region having a predetermined edge is extracted for each of adjacent images, a plurality of images are bonded to one another, and one high-resolution image is generated. Also, there is known an image display device (see, for example, Japanese Patent Application Laid-Open No. 2004-275361) which generates line images in which geometric characteristics of a subject are represented by line drawing for each of medical images, and displays the line images for a plurality of medical images by superimposing them on each other, thereby making it easy to compare the geometrical characteristics of the subject in the medical image which is a diagnosis object.
Furthermore, there is also known a measurement processor including a measurement point setting device which automatically sets a measurement point for geometrically measuring a measurement object image based on the positional information of the measurement points which are set with respect to the measurement object images photographed at different time points which are obtained by photographing substantially the same region of the same subject in time sequence, and the measurement reference images corresponding to them, and a geometrical information measuring device which geometrically measures the measurement object image based on the positional information of the measurement points set with respect to the measurement object images, so as to keep an eye on developments of the state of the disease of a patient (see, for example, Japanese Patent Application Laid-Open No. 2002-203248).
Further, conventionally, quantification of evaluation of a space of a joint has been performed in order to provide doctors with objective diagnosis information so that the doctors can perform more accurate diagnosis or judgment, and there is known a technique of obtaining upper side and lower side of a region where a cartilage of a knee exists from X-ray image data, and the range in the lateral direction where the cartilage of the knee exists from the X-ray image data, regarding the region surrounding by the upper side and the lower side obtained in the above description in the range in the lateral direction as a region where the cartilage exists, and acquiring a size (square measure) of the region where the cartilage exists (see, for example, Japanese Patent Application Laid-Open No. 2008-93229). Namely, in this case, the size of the region where the cartilage exists corresponds to the size of the space of the joint, and therefore, the space narrowing extent based on the size of the region where the cartilage exists, which is thus acquired, is quantified.